> ## Documentation Index
> Fetch the complete documentation index at: https://upstash.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# $cardinality

`$cardinality` returns the number of distinct values in a field.

All matching field values are deduplicated, then counted.

If `missing` is provided, documents without the field are treated as that fallback key
(which can increase the distinct count by at most one extra value).

### Compatibility

| Field Type  | Supported |
| ----------- | --------- |
| TEXT        | No        |
| U64/I64/F64 | Yes       |
| DATE        | Yes       |
| BOOL        | Yes       |
| KEYWORD     | Yes       |
| FACET       | No        |

Field must be `FAST`.

### Arguments

| Argument  | Type               | Required | Description                      |
| --------- | ------------------ | -------- | -------------------------------- |
| `field`   | `string`           | Yes      | Field to aggregate.              |
| `missing` | `string \| number` | No       | Fallback key for missing fields. |

<Tabs>
  <Tab title="TypeScript">
    ```ts theme={"system"}
    await index.aggregate({
      aggregations: {
        unique_users: { $cardinality: { field: "userId" } },
      },
    });
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={"system"}
    index.aggregate(
        aggregations={"unique_users": {"$cardinality": {"field": "userId"}}}
    )
    ```
  </Tab>

  <Tab title="Redis CLI">
    ```bash theme={"system"}
    SEARCH.AGGREGATE events '{}' '{"unique_users": {"$cardinality": {"field": "userId"}}}'
    ```
  </Tab>
</Tabs>

### Output

```json theme={"system"}
{ "unique_categories": { "value": 3 } }
```